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      <title>熔断和降级的区别 - 交互式测验</title>
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      <div class="main-wrapper">
          <div class="quiz-container">
            <div class="quiz-header">
              <h1>熔断和降级的区别 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
            <div id="quiz-content">
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      <script>
        const quizData = [
  {
    "question": "根据文档，服务熔断 (Circuit Breaking) 和服务降级 (Service Degradation) 的核心区别是什么？",
    "options": [
      "熔断是为了降低系统负载，而降级是为了提高响应速度。",
      "熔断是直接切断对故障服务的调用以防止故障蔓延，而降级是在服务异常时提供替代方案来保证核心功能可用。",
      "熔断是永久性地关闭服务，而降级是临时性的。",
      "熔断通常由Netflix Hystrix实现，而降级由Sentinel实现。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "熔断的核心思想是“断开”，像电路断路器一样，在检测到服务持续失败后，主动切断请求链路，防止故障扩散，保护整个系统。而降级的核心思想是“退而求其次”，当服务不可用或资源紧张时，提供一个功能简化的备用方案（如返回缓存数据或默认值），以确保核心业务不中断，维持基本的用户体验。",
    "source": "文档中「熔断和降级的区别」部分",
    "hint": "可以把熔断想象成电路中的“保险丝”，而降级则像是汽车的“备用轮胎”。它们应对问题的策略是不同的。"
  },
  {
    "question": "在服务熔断机制中，当熔断器处于“半开状态 (Half-Open State)”时，它的主要作用是什么？",
    "options": [
      "允许所有请求正常通过，同时重置失败计数器。",
      "完全阻止所有请求，以给下游服务足够的时间恢复。",
      "允许少量“探测”请求通过，以判断下游服务是否已经恢复正常。",
      "立即执行降级策略，返回一个预设的错误响应。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "半开状态是熔断器从“打开”到“关闭”的过渡阶段。在熔断窗口期结束后，熔断器进入此状态，它会尝试性地放行一部分请求去调用下游服务。如果这些请求成功，说明服务可能已恢复，熔断器就会切换回“关闭”状态；如果依然失败，则会再次切换回“打开”状态，继续保护系统。",
    "source": "文档中「服务熔断」下的「3. 半开状态（Half-Open State）」部分",
    "hint": "文档中提到，在熔断窗口期结束后，熔断器需要一种机制来“检测目标服务是否恢复正常”。"
  },
  {
    "question": "根据熔断器的工作原理，什么情况会导致熔断器从“关闭状态 (Closed State)”切换到“打开状态 (Open State)”？",
    "options": [
      "在设定的时间窗口内，服务调用失败的次数或失败率超过了预设的阈值。",
      "熔断窗口期结束，并且探测请求成功。",
      "所有请求都调用成功，系统负载恢复正常。",
      "系统管理员手动触发了熔断开关。"
    ],
    "correctAnswerIndex": 0,
    "explanation": "在“关闭状态”下，熔断器允许所有请求通过，并持续监控调用结果。它内部维护着一个失败计数器或失败率统计。一旦在统计周期（如滑动窗口）内，失败指标达到了预先设定的阈值，就意味着下游服务出现了严重问题，此时熔断器会自动“跳闸”，切换到“打开状态”以阻断后续请求。",
    "source": "文档中「服务熔断」下的「1. 关闭状态（Closed State）」部分",
    "hint": "在“关闭状态”下，熔断器扮演着“哨兵”的角色，它会监控什么指标来决定是否需要采取行动？"
  },
  {
    "question": "以下哪一项不是文档中明确提到的触发“服务降级”的典型条件？",
    "options": [
      "某个服务的响应时间超过了预设阈值。",
      "某个服务的调用失败率持续过高。",
      "系统资源（如CPU、内存）使用率接近饱和。",
      "外部依赖的服务发布了不兼容的新版本。"
    ],
    "correctAnswerIndex": 3,
    "explanation": "服务降级通常是应对系统当前“运行时”的异常状态。文档中明确列出的触发条件包括：服务响应过慢、服务故障率过高、系统整体资源紧张。而外部服务版本更新虽然也可能导致问题，但它更偏向于一个部署或兼容性问题，而不是降级机制通常自动应对的实时性能或可用性指标。",
    "source": "文档中「服务降级」下的「降级的触发条件」部分",
    "hint": "服务降级机制关注的是系统实时的健康状况，如性能指标和资源使用情况。"
  },
  {
    "question": "当一个电商网站的实时个性化推荐服务响应缓慢时，系统决定不等待其结果，而是直接返回一个预先缓存的“上周热销商品”列表。根据文档，这最符合哪种降级策略？",
    "options": [
      "静态降级 (Static Degradation)",
      "服务替代 (Service Substitution)",
      "缓存降级 (Cache Degradation)",
      "降级比例 (Degradation Ratio)"
    ],
    "correctAnswerIndex": 2,
    "explanation": "缓存降级策略的核心在于，当实时服务出现问题（如响应过慢或不可用）时，系统会返回一个预先缓存好的、可接受的数据副本作为替代。这个例子中，“上周热销商品”列表就是一个缓存数据，它保证了用户界面的完整性和基本功能，避免了因等待实时推荐而造成的糟糕体验。",
    "source": "文档中「服务降级」下的「降级策略」部分",
    "hint": "文档中描述了一种策略：当服务响应时间过长时，返回“之前缓存的数据”来避免用户长时间等待。"
  },
  {
    "question": "在熔断器的“打开状态 (Open State)”下，系统会如何处理新的服务调用请求？",
    "options": [
      "将请求放入一个延迟队列中，等待服务恢复后再处理。",
      "允许一小部分请求通过以测试服务健康状况。",
      "立即拒绝请求并快速返回一个预设的错误或降级响应。",
      "尝试调用一个地理位置上更近的备用服务实例。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "一旦熔断器进入“打开状态”，其主要职责就是“断开”电路。这意味着所有到达该熔断器的请求都会被立即拒绝，不会被转发到下游已经出现故障的服务。系统会直接返回一个预定义的错误或执行降级逻辑，这样做既能保护下游服务免受进一步冲击，也能让上游调用方快速失败，避免资源被长时间占用。",
    "source": "文档中「服务熔断」下的「2. 打开状态（Open State）」部分",
    "hint": "文档提到，在“打开状态”下，“所有请求都会被立即拒绝”。"
  },
  {
    "question": "无论是服务熔断还是服务降级，它们作为分布式系统中的容错机制，其共同的最终目标是什么？",
    "options": [
      "彻底消除服务间调用的所有失败可能性。",
      "提升系统在正常运行状态下的峰值处理能力。",
      "防止局部或单个服务的故障扩散，避免引发整个系统的连锁反应（雪崩效应），从而提高系统整体的稳定性和可用性。",
      "降低微服务的开发复杂度和运维成本。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "熔断和降级的根本目的都是提升系统的韧性（Resilience）。在复杂的分布式环境中，单个服务的故障是不可避免的。这两种机制通过不同的方式（隔离故障或提供备用方案）来控制故障的影响范围，确保即使在部分组件失效的情况下，整个系统依然能够对外提供核心服务，从而避免了灾难性的系统性崩溃。",
    "source": "文档中开篇「熔断和降级的区别」及各自「优势」部分",
    "hint": "回想一下文档开篇提到的“任何一个小小的故障都有可能引发连锁反应，最终导致整个系统的瘫痪”。这些机制正是为了解决这个问题。"
  }
];
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          optionsListEl.innerHTML = '';
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            resultBox.className = `result-box ${isCorrect ? 'correct' : 'incorrect'}`;
            
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            const currentQuestion = quizData[currentQuestionIndex];
            if (currentQuestion.hint) {
                hintContainerEl.textContent = currentQuestion.hint;
                hintContainerEl.style.display = 'block';
            } else {
                hintContainerEl.style.display = 'none';
            }
        }

        function showFinalScore() {
            document.querySelector('.quiz-body').style.display = 'none';
            document.getElementById('quiz-footer').style.display = 'none';

            const correctCount = score;
            const totalQuestions = quizData.length;
            const answeredCount = userAnswers.filter(a => a !== null).length;
            const wrongCount = answeredCount - correctCount;
            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

            const finalScoreHtml =
                '<div class="final-score-container">' +
                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  